1、BRITISH STANDARD BS3762-3.25: 1989 Analysis of formulated detergents Part3: Quantitative test methods Section3.25 Methods for determination of water and volatile matter content NOTEIt is recommended that this Section be read in conjunction with the information in the “General introduction”, publishe
2、d separately as BS3762-0. UDC 661.185:543BS3762-3.25:1989 This BritishStandard, having been prepared under the directionof the Chemicals Standards Policy Committee, waspublished under the authorityof the Board of BSI andcomes into effect on 29September1989 BSI 12-1999 The committees responsible for
3、this BritishStandard are shown inPart0. The following BSI references relate to the work on this standard: Committee referenceCIC/34 Draft for comment88/52266DC ISBN 0 580 17368 2 Foreword This Section of BS3762 has been prepared under the direction of the Chemicals Standards Policy Committee and sup
4、ersedes method D14 of BS3762:1964, which is withdrawn. This Section describes methods of test only and should not be referred to as a specification defining limits of purity. Reference to the standard should indicate that the method of test used is in conformity with BS3762-3.25. A British Standard
5、does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an i
6、nside front cover, pagesi andii, pages1 to4, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date
7、 of issue CommentsBS3762-3.25:1989 BSI 12-1999 i Contents Page Foreword Inside front cover 1 Scope 1 2 Method1. Entrainment 1 3 Method2. Oven drying 2 4 Method3. Karl Fischer 3 5 Test report 4 Publications referred to Inside back coverii blankBS3762-3.25:1989 BSI 12-1999 1 1 Scope This Section of BS
8、3762 describes methods for determining the content of water or volatile matter in formulated detergents. NOTE 1The water determined may include water of crystallization. Method1 is for determination of water in samples that do not contain volatile compounds that are miscible with water, for example,
9、 low molecular mass alcohols. Method2 is for determination of the loss in mass on heating at150 C, which indicates the volatile matter content; the result will be the water content if water is the only volatile compound in the sample. Method3 is for determination of water in liquids and in pastes an
10、d solids that release all their water during the titration of a solution or a dispersion in methanol; it is not applicable to samples that contain noticeable amounts of oxidizing agents, ketones, strong acids or strong bases. NOTE 2The titles of the publications referred to in this Section are liste
11、d on the inside back cover. 2 Method1. Entrainment 2.1 Principle The water present in a test portion is entrained by azeotropic distillation with xylene, and the volume of water collected is measured. 2.2 Reagents The reagents shall be of a recognized analytical grade. Water complying with grade3 of
12、 BS3978 shall be used throughout. 2.2.1 Xylene 2.2.2 Calcium stearate, anhydrous. NOTEAnhydrous sodium acetate may be substituted for anhydrous calcium stearate. 2.2.3 Ammonium hexanitratocerate(IV) solution. Dissolve20g of ammonium hexanitratocerate(IV) in about60mL of water. Add25mL of nitric acid
13、 solution70%(m/m) HNO 3 and dilute to100mL. NOTEThis solution may be prepared in proportionately smaller quantities if preferred. 2.3 Apparatus Ordinary laboratory apparatus and the following are required. 2.3.1 Dean and Stark apparatus, complying with BS756, type1, having a distillation flask of500
14、mL capacity and a2mL receiver (for solids) or a7.5mL receiver (for liquids and pastes). 2.3.2 Boiling aid, for example pumice stone fragments. 2.4 Procedure Thoroughly dry the flask and the receiver, using an oven or a current of warm air. Weigh between7g and20g of sample, to the nearest0.01g, into
15、the flask ensuring that the expected water content does not exceed the capacity of the receiver. Add100mL to150mL of the xylene(2.2.1) to the flask. Add1g to2g of the anhydrous calcium stearate or sodium acetate(2.2.2). Dry the inner surface of the condenser by pushing a plug of absorbent cotton thr
16、ough it, then connect it to the receiver and flask. Heat the flask and contents using an electric heating mantle or an oil bath so that the contents boil and condensate falls from the condenser at a rate of2 to5 drops per second. After at least30min and when the distilled xylene is clear and the vol
17、ume of water in the receiver no longer increases, stop heating and allow the apparatus to stand long enough for the water to separate completely. If drops of water adhere to the tube or the condenser, use a long stout wire or a spray of xylene to dislodge them and combine them with the water in the
18、receiver. Read the volume of water collected. NOTETo test for the presence of volatile alcohols, transfer the water layer, or part of it, to a small test tube and place a similar quantity of distilled water, or water of equivalent purity, into a second tube for comparison. Add to each an equal volum
19、e of the ammonium hexanitratocerate(IV) solution(2.2.3) and mix. An orange colour in the sample tube, when compared with the yellow of the blank, indicates that alcohols are present and that method1 is inapplicable.BS3762-3.25:1989 2 BSI 12-1999 2.5 Expression of results The water content, expressed
20、 as a percentage by mass, is given by the following expression: NOTEIt is assumed that the density of water, at the temperature when the volume is read, is exactly1g/mL within the accuracy of the determination. 2.6 Precision No precision data are available. 3 Method2. Oven drying 3.1 Principle The l
21、oss of mass, on heating at150 C for2h, is determined. 3.2 Apparatus Ordinary laboratory apparatus and the following are required. 3.2.1 Dish or beaker, of glass or porcelain, of capacity not exceeding100mL. 3.2.2 Oven, ventilated, capable of being controlled at150 5 C. 3.3 Procedure Ensure that the
22、dish or beaker(3.2.1) is dry, then weigh to the nearest0.001g. NOTE 1Some dry, coarse sand or other stable material may be contained in the dish or beaker to accelerate the subsequent drying operation. Add2g to3g of sample and reweigh to the nearest0.001g. Place the dish or beaker in the oven(3.2.2)
23、 at150 5 C for2h NOTE 2If desired the dish or beaker may first be heated on a steam-bath under a stream of air until most of the water has evaporated. Allow the dish or beaker and contents to cool in a desiccator and then reweigh to the nearest0.001g. 3.4 Expression of results The loss in mass on he
24、ating at150 C, expressed as a percentage by mass, is given by the following expression: NOTEIf water is the only volatile compound liable to be present, the result may be expressed as “water content”. 3.5 Precision Intralaboratory studies have given the following values for liquid detergents (see BS
25、5497-1): where V is the volume of water collected in the receiver (inmL); m is the mass of the test portion (ing). where m 1 is the mass of the empty dish or beaker (ing); m 2 is the mass of the dish or beaker plus sample (ing); m 3 is the mass of the dish or beaker plus dried contents (ing). Water
26、content Repeatability Lower than30% 0.3% absolute Not lower than30% 1% relative V 100 m - m 2 m 3 m 2 m 1 -100 BS3762-3.25:1989 BSI 12-1999 3 4 Method3. Karl Fischer 4.1 Principle A solution or dispersion of the detergent is titrated with Karl Fischer reagent using an electrometric method to determi
27、ne the end point. Karl Fischer reagent is a solution containing a methosulphite and iodine, the former being created by mixing the components: B+CH 3 OH+SO 2 =BH.CH 3 SO 3 (B is a base, typically pyridine.) In the presence of water, the methosulphite ion is oxidized to methosulphate, the reaction be
28、ing quantitative in the presence of a suitable buffering agent, for example pyridine plus1-ethyl piperidine: BH.CH 3 SO 3 +I 2 +H 2 O+2B=BH.CH 3 SO 4+2BH.I At the end-point a slight excess of iodine will depolarize an electrode pair placed in the solution and allow a current to flow and move a galva
29、nometer needle, or some other detector. 4.2 Reagents The reagents shall be of a recognized grade for the determination of water using Karl Fischer reagent. 4.2.1 Karl Fischer reagent, of concentration such that1mL is equivalent to about5mg of water. NOTEVarious Karl Fischer reagents, some of which a
30、re pyridine-free, are available commercially and may be used. Alternatively, Karl Fischer reagent may be prepared as described in2.4 of BS2511:1970. 4.2.2 Methanol, water contentu 0.02%(m/m). NOTEMethanol specially dried for use with Karl Fischer reagent is available commercially. 4.2.3 Sample solve
31、nt for pyridine-free Karl Fischer reagent, as recommended by the supplier of the pyridine-free Karl Fischer reagent. 4.2.4 Water, complying with grade3 of BS3978. 4.3 Apparatus 4.3.1 Manual or semi-automatic Karl Fischer apparatus, comprising a burette of size10mL to50mL, a Karl Fischer reagent rese
32、rvoir, a titration vessel, a stirrer, and an electrical circuit to detect the end-point. The titration vessel shall have a stoppered side inlet for introducing samples and a stopcock for drainage. The apparatus shall be fitted with seals and guard tubes of desiccant to prevent the ingress of atmosph
33、eric moisture. 4.3.2 Syringe, or Lunge-Rey pipette, of minimum capacity0.25mL. 4.3.3 Tube, or other container, for weighing a solid sample and permitting easy transference to the titration vessel. 4.4 Standardization of the Karl Fischer reagent 4.4.1 Standardize the Karl Fischer reagent daily before
34、 use. Follow the same standardization procedure for the pyridine-containing titrant/solvent system and the pyridine-free titrant/solvent system. 4.4.2 Add enough of the appropriate solvent(4.2.2 or4.2.3) to the clean, dry titration vessel to cover the electrodes. NOTEThe volume of solvent depends on
35、 the size of the titration vessel. Seal all openings to the vessel, start the magnetic stirrer and adjust for a smooth stirring action. Turn on the indication circuit and add the Karl Fischer reagent(4.2.1) from the burette until the end point is reached. Swirl the contents of the titration vessel t
36、o remove any water from the inside walls of the vessel. If necessary, run off excess liquid. Carefully add more of the Karl Fischer reagent if needed until a steady end point is just reached and maintained for at least30s. 4.4.3 Into the syringe or pipette(4.3.2) place an amount of the water(4.2.4)
37、equivalent to about half the contents of the Karl Fischer reagent burette, and weigh. Add the contents of the syringe or pipette to the sample solvent in the titration vessel which has been adjusted to the end point. Reseal the vessel immediately, then reweigh the syringe or pipette. Titrate with Ka
38、rl Fischer reagent until a steady end point is reached and maintained for at least30s. Record to the nearest0.01mL the volume of titrant needed to reach the end point.BS3762-3.25:1989 4 BSI 12-1999 4.4.4 Calculate the water equivalent of the Karl Fischer reagent using the expression: F = M/T 4.4.5 R
39、un off sufficient of the contents of the titration vessel to leave the electrodes just covered, then repeat the operations of4.4.3 and4.4.4. 4.4.6 If the two values of F differ by more than2% of their mean, then discard the contents of the titration vessel and repeat steps4.4.2 to4.4.5. NOTEIf there
40、 is difficulty in obtaining results within2% then it is likely that the Karl Fischer reagent or the solvent has deteriorated and fresh supplies should be used. When two values of F agreeing to within2% have been obtained, record the mean asF 2 . 4.5 Determination 4.5.1 Add the solvent to the titrati
41、on vessel and adjust to the end point by proceeding as in4.4.2. NOTEIf the previous titration was for standardization or analysis of a liquid detergent and did not overshoot the end-point, it is sufficient to run out excess liquid until the electrodes are just covered. 4.5.2 Proceed as in4.4.3 using
42、 the sample to be analysed and taking sufficient to yield a titration of between30% and150% of the volume used in standardization. In the case of a solid sample, use the tube(4.3.3) in place of the syringe or pipette(4.3.2). 4.6 Expression of results The water content, expressed as a percentage by m
43、ass, is given by the expression: 4.7 Precision No precision data are available. 5 Test report The test report shall include the following information: a) a reference to this BritishStandard, i.e.BS3726-3.25:1989; b) a reference to the test method used, i.e.method1, method2 or method3; c) the results
44、 expressed in accordance with2.5, 3.4 or4.6; d) a complete identification of the sample. where F is the water equivalent of the Karl Fischer reagent(inmg/mL); M is the mass of water added (inmg); T is the volume of reagent required for titration of the added water (inmL). where T is the titration fr
45、om4.5 (inmL); F 2 is the mean water equivalent of the Karl Fischer reagent (inmg/mL); m is the mass of sample (ing). TF 2 m 10 -BS3762-3.25:1989 BSI 12-1999 Publications referred to BS756, Specification for Dean and Stark apparatus. BS2511, Methods for the determination of water (Karl Fischer method
46、). BS3978, Specification for water for laboratory use. BS5497, Precision of test methods. BS5497-1, Guide for the determination of repeatability and reproducibility for a standard test method by inter-laboratory tests. BS3762-3.25: 1989 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsIns
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